Low-loss waveguiding structures, in particular modulators

Abstract

An optical modulator that uses adiabatic tapers to change the width of the waveguides between multimode waveguides and single mode waveguides on a low-loss, e.g. thin-film lithium niobate, electro-optic platform. The architecture enables the utilization of the fundamental mode of multimode wide optical waveguides that have lower optical propagation loss without sacrificing the benefit of the signal integrity and ease of control of single mode operation.

We claim: 
     
         1 . An optical modulator comprising:
 a first active region supporting a first set of modes of an optical signal; and   a first transitional region converting between the first set of modes and a second set of modes of the optical signal, the second set of modes being different from the first set of modes;   wherein at least a portion of the first active region is configured to provide modulation of the optical signal, the first active region and the first transitional region including lithium; and   wherein at least one of the first set of modes or the second set of modes includes a fundamental mode.   
     
     
         2 . The optical modulator of  claim 1 , wherein the first set of modes and the second set of modes includes the fundamental mode. 
     
     
         3 . The optical modulator of  claim 1 , wherein the first set of modes includes more modes than the second set of modes. 
     
     
         4 . The optical modulator of  claim 1 , wherein the first set of modes include fewer modes than the second set of modes. 
     
     
         5 . The optical modulator of  claim 1 , further comprising:
 a second region, the first transitional region being between the first active region and the second region, wherein the second region includes a bend that is a substantially 1800 Euler bend.   
     
     
         6 . The optical modulator of  claim 5 , wherein the second region has a cross sectional area <3 μm 2 . 
     
     
         7 . The optical modulator of  claim 1 , wherein the first active region and the first transitional region include an electro-optic material with an electro-optic constant >10 pm/V. 
     
     
         8 . The optical modulator of  claim 1 , wherein the first active region and the first transitional region include Lithium Niobate or Lithium Tantalate. 
     
     
         9 . The optical modulator of  claim 1 , further comprising:
 a splitter, optically coupled with the first transitional region, configured to split an input optical signal into a first sub-beam and a second sub-beam; and   a second waveguide arm coupled to the splitter for transmitting the second sub-beam.   
     
     
         10 . The optical modulator of  claim 9 , wherein the first active region transmits the first sub-beam. 
     
     
         11 . The optical modulator of  claim 1 , wherein the first transitional region includes an adiabatic taper. 
     
     
         12 . The optical modulator of  claim 1 , further comprising:
 a set of electrodes adjacent to at least a portion of the first active region.